Polymers polymer-solvent interdiffusion

Equation (8.1) is the continuity equation for the polymer Eq. (8.2) describes the evolution of v due to the BZ reaction and the transport of the catalyst with the movement of the polymer network Recall that the catalyst is tethered to the chains and, thus, does not diffuse through the solution. Equation (8.3) characterizes the changes in u due to the BZ reaction, the transport of this activator with the solvent, and the diffusion of the activator within the solvent We assumed for simplicity that it is solely the polymer-solvent interdiffusion that contributes to the gel dynamics hence, in Eq. (8.3), we took into account that < vfPi + (1 — )vf i = 0, where vf i is the solvent velocity [2]. 

This theory, put forth by Vo)mtskii, accounts for the autoadhesion of polymers by the interdiffusion of polymers across the interface and their mutual solubility. Direct radiometric and luminescence experiments have confirmed that the diffusion boundary may be as deep as 10 pm. Interdiffusion is also important in solvent welding of plastics where the solvent essentially plasticizes the surfaces and... 

In summary, the interdiffusion of polymer chains across a polymer/polymer interface requires the polymers (adhesive and substrate) to be mutually soluble and the macromolecules or chain segments to have sufficient mobility. These conditions are usually met in the autohesion of elastomers and in the solvent welding of compatible, amorphous plastics. In both these examples interdiffusion does appear to contribute significantly to the intrinsic adhesion. However, where the solubility parameters of the materials are not similar, or one polymer is highly crosslinked, crystalline or below its glass transition temperature, then interdiffusion is an unlikely mechanism of adhesion. In the case of polymer/metal interfaces it appears that interdiffusion can be induced and an interphase region created. But this effect enhances the interfacial adhesion by improving the adsorption of the polymeric material rather than by a classic diffusion mechanism. 

Virtually all end-use formulations of latex polymers of MFT much above 5 °C (40 °F) contain a moderately low volatility solvent for the polymer. These act as temporary plasticizers to ensure low MFT and enhance polymer interdiffusion. The solvent should diffuse and evaporate as quickly as possible for film hardness development, but not at the expense of completeness of film strength development A complication is that compositions of high Tg which contain solvent... 

This theory suggests that adhesion is developed through the interdiffusion of molecules in between the adhesive and the adherend. The diffusion theory is primarily applicable when both the adhesive and the adherend are polymers with relatively long-chain molecules capable of movement. The nature of materials and bonding conditions will influence whether and to what extent diffusion takes place. The diffuse interfacial (interphase) layer typically has a thickness in the range of 10-1,000 A (1-100 nm). Solvent cementing or heat welding of thermoplastics is considered to be due to diffusion of molecules. ... 

A comparison of different theories is given under Theories of adhesion. Further considerations of interdiffusion are discussed under Solvent welding, Polymer diffusion reptation and interdigitation and Polymer-poiymer adhesion weid strength. 

Solvent welding and solvent cementing are widely used techniques for the joining of thermoplastic polymers. A small amount of solvent along the joint promotes interdiffusion of polymer chains between the substrates. This creates a permanent weld, with no additional phases or potentially weak interfaces. A solvent cement is a solution of the polymer being joined. This also promotes interdiffusion, and leaves a single-phase joint when the solvent has evaporated. 

Solvent cementing describes a process in which a solution of the polymer being joined is applied to the substrates. This may be preceded by application of a primer (solvent) to the substrate to facilitate interdiffusion. Use of solvent cement can help fill gaps, allowing... 

The interdiffusion of the polymer molecules of adhesive and substrate is dependent upon various parameters, such as pressure, time, temperature, molecule size, and, of course, the reciprocal solubility, as shown by the correlation between the compatibility of the polymers and the quality of the bond [21]. Examples of bonds to which the diffusion theory is applicable include the bonding of PVGU adherents to PVC in solvents containing tetrahydrofuran and so-called contact bonding, where the diffusion... 

Numerous possibilities exist for the manufacture of polymers with latent coreactive sites °l The introduction of built in functional groups onto the surface of the polyurethane particle and proprietary reactive groups copolymerised into the backbone of the acrylic and buried deep into the core of the acrylic phase are the usual techniques for crosslinkable copolymer type systems. The crosslinking mechanism is not fully understood, but it is assumed to be made possible via interdiffusion of polymer chains across the former boundaries of adjacent particles. Evidence for the crosslinking can be found in increased solvent resistance, softening temperature and the appearance of a single Tg.. 

Here 5 is the solvent concentration and n the (normal) distance from the advancing interface. The far field (bulk) solvent concentration is and for convenience the concentration of solvent at the crystal-solution interface is assigned the equilibrium value 5/, these can be described equivalently in terms of the polymer concentrations if desired. The interdiffusion coefficient... 

---